A self-tightening drill chuck has a chuck body, a tightening sleeve that can rotate coaxially to the chuck body, and a jaw holder supported on the chuck body in which jaws are guided in guide slots. The jaws can be adjusted by the jaw holder by a relative rotation between the chuck body and the tightening sleeve for tensioning and loosening. A locking device comprises an annular array of teeth coaxial with the chuck axis and a pawl that engages under the force of a spring into the gear ring and is supported on the jaw holder. This locking device locks the chuck body and the first pawl against relative rotations for loosening the jaws when the first pawl has engaged into the teeth but does not hinder relative rotation tightening. A stop formation on the jaw holder and a counterstop formation on the tightening sleeve limit relative rotation of the tightening sleeve relative to the jaw holder between a first rotational end position corresponding to the engaged state or locking position of the first pawl and to a second rotational position corresponding to the disengaged state or a freeing position. A latch with a seat associated with the first rotational position and with another seat associated with the second rotational position is provided between the jaw holder and the tightening sleeve. This latch does not release rotation of the tightening sleeve relative to the jaw holder at the least in the tightening direction until a predetermined tensioning force has been achieved.
The pawl and teeth are therefore oriented as described in WO 2006/111114 such that the torque applied as a back force against the chuck during normal drilling tends to rotate the sleeve and parts in the tightening direction so that the chuck self tightens. The problem with this type of operation is that the chuck can get so very tight that it is very difficult or impossible to loosen it by hand. The user must get tools to dechuck the tool, typically a drill bit, held by the jaws.